This application claims priority from Irish Patent Application No. S2001-0543, filed on Jun. 5, 2001, by Joseph Dillon, entitled A SHEARBAR FOR A FORAGE HARVESTER.
This invention relates to a shearbar for a forage harvester.
When harvesting forage material such as grass, maize and other standing plants, the plant material is first cut from its root, close to the ground, and then conveyed into the forage harvester to a rotary cutter. The rotary cutter is typically a drum carrying a series of knives whose purpose is fine chopping of the crop conveyed into the harvester. The shearbar is located such that in use the knives successively approach the shearbar at an angle to cut the maize or other crop at the edge of the shearbar by a scissors-like action. The edge of the shearbar thus acts as a fixed counter knife to the knives of the rotary cutter.
When the plant material is conveyed into the machine it passes over and wears the top surface of the shearbar. Also, the cutting action and crop flow on the cutting edge of the shearbar contributes to wear and dulling of the shearbar edge. Depending on the plant material being harvested there can be significant wear in a relatively short space of time. This can be exacerbated by sand and grit on the leaves and stalks of the crop.
As a method of preventing or slowing wear, the industry has applied a wear resistant coating (cladding) known as hardfacing to the top surface of the shearbar, such hardfacing extending to the cutting edge. For example, a top coating of tungsten or chromium carbide, or other carbide-based hardfacing, in the region of 1-2 mm thick has been used.
The top coating of hardfacing when ground or machined to the desired size of the finished part provides a square edge for the knives on the drum to cut against. It also provides significant wear protection against erosion caused by a large volume of abrasive plant matter passing over the top of the shearbar. The sharp square edge is important for reduction of the load on the machine required to cut the crop and also in prolonging the life of the knife and the shearbar.
A problem with this construction is the development of a wear gully on the vertical side of the shearbar below the cutting edge of the wear resistant coating. This wear gully appears in the main body of the shearbar which is typically made of a mild steel, a medium carbon alloy steel of relatively low hardness or a plain carbon steel of low hardness. As the worn area increases in depth and size, the cutting edge of the coating becomes unsupported underneath and projects freely from the main body of the shearbar. When unsupported, the coating can chip when it comes into impact with items such as stones or foreign objects picked up by the harvester.
It is an object of the present invention to avoid or mitigate this problem.
According to the present invention there is provided a shearbar comprising an elongated steel body having a top surface covered with a layer of hardfacing material along at least one longitudinal edge to act as a counter knife to a rotary cutter, the body having a region extending along and immediately below the longitudinal edge of the hardfacing layer, the region having a hardness intermediate that of the steel body and the hardfacing layer.
In one embodiment the said region is an inlay. In another embodiment it is a locally heat-hardened portion of the body.
The introduction of an inlay or heat-hardened portion below the edge of the hardfacing layer prolongs the life of the shearbar as it xe2x80x98bridges the gapxe2x80x99 in wear resistance between the relatively soft steel body and the very hard hardfacing material.
In the case of an inlay it is preferably made of high alloy or xe2x80x98toolxe2x80x99 steel, most preferably with hardness of from 40 to 70 Hrc. The use of xe2x80x98toolxe2x80x99 steel has the added advantage of high impact resistance, enhancing the performance of the shearbar under a range of harvesting conditions. This performance enhancement would not be achievable with thermal sprayed hardfacing or PTA deposit hardfacing which are common in the industry.
Various prior examples of shearbars are shown in (a) to (i) of FIG. 5, none of which solve the foregoing problem or do not do so except at considerable expense. The drawings shown in FIG. 5 are cross-sectional views of shearbars which are highly elongated in the direction normal to the plane of the drawing.
FIG. 5(a): Metal coatings 0.2 mm-0.3 mm or 0.6 mm-0.9 mm thick sprayed on the top edges of the shearbar.
FIG. 5(b): Metal hardfacing 0.6 mm-0.9 mm thick sprayed on side edges of shearbar.
FIG. 5(c): Tool steel inlay on corners of shearbar by submerged arc welding. Alternatively, hardfacing on corners with PTA (Plasma Transferred Arc) welding.
FIG. 5(d): Cladding or hardfacing or Brazecoat M hardfacing (from Innobraze GmbH) on top surface.
FIG. 5(e): Sprayed on hardfacing on vertical edges and on centre of top surface.
FIG. 5(f): Hardfacing 0.4 mm-1 mm thick inlaid in centre of top surface and edge deposits of 1.2 mm-1.4 mm thick PTA.
FIG. 5(g): Heavy side edge hardfacing both inlayed and protruding, typically up to 3 mm thick.
FIG. 5(h): Heavy top edge hardfacing both inlayed and protruding, typically up to 3 mm thick. This corresponds to EP 8291198.
FIG. 5(i): Similar to (f) with edge hardfacing typically up to 3 mm thick both protruding and inlaid.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: